If a threaded coupling is properly designed, the male portion will always fail first. Further, the stress on the material will be below the fatigue limit, meaning it can withstand, theoretically at least, an infinite number of torque cycles.
Torque-To-Yield (TTY) fasteners are different, in that they are designed to be installed with a predetermined stretch, or yield, of the bolt that is beyond the plastic, or proportional limit. Since, the stretch is beyond the priportional limit they will retain the stretch after disassembly, and why they should not be reused.
If you look at the graph below you can see the benefits of TTY fasteners. The clamping force of a bolt is proportional to the stress and stress is proportional to the torque, so when normal bolts are torqued below the proportional limit small variations in torque will result in variations in clamping force. However, once the bolt goes into the plastic range, you can have large variations in rotation of the bolt and maintain a constant clamping force. This greatly simplifies high volume assembly where a uniform clamping load is required (such as engine heads).
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